The present invention relates to an ophthalmic lens structure embodying two adjacent layers of dissimilar, organic plastic materials. It further relates to problems that arise in producing such structures. More particularly, the problems tend to arise when at least one of the materials is present in monomeric form, and must be cured in situ.
One such lens structure is described in U.S. Pat. No. 5,232,637 (Dasher et al.). That patent describes a method of producing a glass-plastic, laminated, ophthalmic lens structure. The method comprises applying an organic plastic adhesive layer, for example, a thermoplastic urethane, to a glass lens element which is then inserted in a mold. Thereafter, a monomeric formulation, which may for example be an epoxy formulation, is flowed onto the adhesive layer and cured in situ to form a laminated lens blank. In the course of developing this method, it was discovered that certain deleterious changes could develop in the organic materials during the curing process. These changes were manifested as striae and/or low adhesive strength.
Other situations where the potential exists for similar problems to arise are disclosed in U.S. Pat. No. 5,223,862 (Dasher et al.) and No. 5,254,000 (Friske et al.).
The former application describes forming a segment member composed of an organic material. The segment is formed in a countersink in the surface of an organic lens member. The resulting composite may, in turn be adhered to a thin glass lens member. The latter patent describes production of an organic lens wherein an organic monomer is cast and cured in a plastic mold. The mold may, for example, be composed of a polyolefin plastic material. The lens material cast in the mold may be an epoxide, or an allylic carbonate, in monomeric form. In each of these situations, as well as others that will become apparent, there is a structure wherein layers of adjacent, dissimilar organic materials are present. Further, at least one of the materials may be cured under thermal influence in producing a final product. Thus, the potential for defect development exists in these structures as well.
It is then a basic purpose of the present invention to provide a solution to this problem of defects. It is a further purpose to provide an improved, laminated, ophthalmic lens structure embodying two adjacent layers of dissimilar organic materials. Another purpose is to provide an improved method of producing such a structure wherein at least one of the materials must be thermally cured in situ.